The present invention relates to pilot warning systems and, more particularly, to a system for communicating an elevation of a target aircraft relative to the aircraft in which the system resides. Even more particularly, the present invention relates to a pilot warning system in which a bearing of nearby aircraft is enabled or inhibited depending on whether or not the nearby aircraft are traveling at an altitude which may result in collision with the aircraft carrying the system.
In my prior U.S. Pat. Nos. 5,506,590; 5,223,847 and 5,861,846, the disclosures of which are herein incorporated by reference, I disclosed systems for determining relative bearing and elevation of a nearby aircraft using passive reception of beacon transponder emissions or distance measuring equipment from the nearby aircraft. Relative bearing is determined by time relationships of transponder signals received on a plurality of antennae on a surface of the aircraft. Relative altitude is determined using vertically separated antennae, generally one on an upper surface, and one on a belly surface. The relative altitude is found in a comparison of the times of arrival of a signal at the upper and lower antennae.
In a single-signal environment, characteristic of areas with low air traffic, signals from the vertically separated antennae may be satisfactory for determining elevation by measuring differences in time of arrival of the signal at the upper and lower antennas. However, I have discovered that, in busy air traffic terminal control areas, time-of-arrival elevation determination is complicated by substantial overlapping of transponder signals from the many aircraft which are interrogated substantially simultaneously.
In addition to the time-of-arrival interference for vertical measurement, I have discovered that, in busy terminal control areas, bearing indications occur so frequently that it is difficult, even with the directional clues provided by my prior disclosures, to pinpoint a possibly dangerous collision risk.
It is an object of the invention to provide a system for the detection of the relative elevation of a target aircraft from a subject aircraft relative to the deck plane of the subject aircraft.
It is a further object of the invention to provide a system which can determine the relative elevation of a target aircraft from a subject aircraft relative to an inertial horizontal plane.
It is a still further object of the invention to provide a gating system for enabling display of a detected azimuth of a target that may be a collision risk only when a determination is made that the target is located relatively close to the altitude of the aircraft carrying the system, and inhibiting display of targets that are too high above, or too far below, to represent a danger.
Briefly stated, the present invention provides an elevation angle detection device which uses signals from first and second of oppositely pointing antennas to determine an elevation angle of an emitting source. The signal from the second antenna is inverted and phase-compared with the direct signal from the first antenna. The first and second antennas are physically displaced along their axes by about xe2x85x9c electrical wavelengths to establish a sensitive angular region of about xc2x17 degrees. In one embodiment of the invention, the phase of the signal from the first antenna is phase delayed slightly before being applied to the phase detector. This displaces the sensitive angular region upward. The phase of the signal from the second antenna is phase delayed slightly before being applied to a second phase detector. The signal from the first antenna is applied to the second phase detector without being phase delayed. This displaces the sensitive angular region downward. The sensitive angular regions produced by the first and second phase detectors overlap centered on a plane normal to the axes of the first and second antennas. The simultaneous presence of a second emitting source in the overlap is used to detect a crisis collision possibility.
Briefly stated, the present invention provides an elevation angle detection device which uses signals from first and second oppositely pointing antennas to determine an elevation angle of an emitting source. The signal from the second antenna is inverted and phase-compared with the direct signal from the first antenna. The first and second antennas are physically displaced along their axes by about xe2x85x9c electrical wavelengths to establish a sensitive angular region of about xc2x17 degrees. In one embodiment of the invention, the phase of the signal from the first antenna is phase delayed slightly before being applied to the phase detector. This displaces the sensitive angular region upward. The phase of the signal from the second antenna is phase delayed slightly before being applied to a second phase detector. The signal from the first antenna is applied to the second phase detector without being phase delayed. This displaces the sensitive angular region downward. The sensitive angular regions produced by the first and second phase detectors overlap centered on a plane normal to the axes of the first and second antennas. The simultaneous presence of an emitter in the overlap is used to detect a crisis collision possibility.
According to an embodiment of the invention, there is provided an antenna comprising: a first quarter-wave whip pointing in a first direction, a second quarter-wave whip pointing in a second direction opposite to the first direction, axes of the first and second quarter-wave whips being substantially collinear, a base of the first quarter-wave whip being spaced along the axis from a base of the second quarter-wave whip a distance effective to establish a desired relationship between phases of signals received on the first and second quarter-wave whips.
According to a feature of the invention, there is provided an elevation angle detection system comprising: a first antenna disposed in a first direction, a second antenna disposed in a second direction opposite the first direction, a phase inverter attached to the second antenna, the phase inverter producing a phase delay substantially equal to 180 electrical degrees at on operating frequency to produce a phase-delayed signal, a phase detector receiving a signal from the first antenna and the phase-delayed signal, and an output of the phase detector indicating the presence of an emitting source within a predetermined angle of a normal plane to the first and second directions.
According to a further feature of the invention, there is provided an alerting system comprising: a first antenna disposed in a first direction, a second antenna disposed in a second direction opposite the first direction, a phase inverter attached to the second antenna, the phase inverter producing a phase delay substantially equal to 180 electrical degrees at on operating frequency to produce a phase-delayed signal, a phase detector receiving a signal from the first antenna and the phase-delayed signal, an output of the phase detector indicating the presence of an emitting source within a predetermined angle of a normal plane to the first and second directions, a bearing angle detection device for detecting a bearing angle of the emitting source, and a suppression device effective for suppressing output of the bearing angle detection device when the emitting source is outside the predetermined angle, and for enabling the output of the bearing angle detection device when the emitting source is within the predetermined angle.
According to a further feature of the invention, there is provided an alerting system comprising: a first antenna disposed in a first direction, a second antenna disposed in a second direction opposite the first direction, a phase inverter attached to the second antenna, the phase inverter producing an inverted signal substantially inverted by about 180 electrical degrees at on operating frequency to produce a phase-inverted signal, a first phase detector receiving a signal from the first antenna, a first phase delay phase delaying the phase-inverted signal to produce a phase-delayed phase-inverted signal, the phase-delayed phase-inverted signal being applied to a second input of the first phase detector, a second phase detector receiving the phase-inverted signal at a first input, a second phase delay phase delaying the signal from the first antenna to produce a second phase-delayed signal, the second phase-delayed signal being applied to a second input of the second phase detector, a first AND gate responsive to a simultaneous output of the first and second phase detectors for producing a first output, a second AND gate responsive to a simultaneous output of the first phase detector and an absence of an output of the first AND gate for producing a second output, and a third AND gate responsive to a simultaneous output of the second phase detector and an absence of an output of the first AND gate for producing a third output.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.